Futaba GY401 w/ Futaba 9C
Gyro How-to

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Mount the Gyro on the back plate behind the main shaft. Yes, the tape that comes with the gyro is not very cushiony, but that's the way it needs to be. The cushioning is done inside the gyro. The tape works great, use it. As you can see in the picture to the left, I mounted it with the cords coming out toward the back of the helicopter.
Make the connections just as shown in the manual (picture to the left comes from the manual). This is very simple, nothing special here, just connect the rudder servo to the female connector. That leaves two other connectors, one with 3 wires and the other with 1 wire. Connect the one with 3 to the rudder channel 4 on the receiver. Then plug the 1 wire connector into channel 5 - make sure the yellow wire is on the signal side. The signal side will be opposite of the black (ground) side.
  Before we continue it helps to understand the characteristics of this gyro. You have to start up this gyro in heading hold mode. Also as with all heading hold gyros you have to wait for the gyro to initialize after power up before you can move the helicopter. This gyro initializes fast, only about 3 or 4 seconds. Also when using a digital servo like the Futaba 9253 you need to flip the tiny switch on top of the gyro to "on", the swith is labeled "DS".
Common misconception of all heading hold gyros Another thing that a lot of people don't understand is that the rudder travel adjust (ATV's / EPA's) does not adjust how far the servo moves. You cannot use this to prevent linkage binding. This adjustment only effects how fast the tail moves (your pirouette rate).
radio setup For this setup we will make switch 'B' to control the gyro mode. To do this you need to get in the menu system by holding the 'Mode' button down for one second. This gets you in the basic menu then press 'Mode' once to get to the advanced menu. Use the jog wheel to get to the 'GYRO SENS' function. Set the mode to 'GY'. Set the 'rate up' to AVC100 and the down rate to NOR100. And set SW to 'B'.
zero out anything that would effect the rudder In the advanced menu go to 'REVO MIX'. Select Mix and set to 'INH'.
zero center position Go to the 'Sub-trim' menu and set 'RUD' and 'GER' to 0.
Also make sure the trims are centered.
set pirouette speed Go to the 'E. POINT' menu and set 'RUD' to 70%. Hold the rudder stick to the left and set the value to 70%, hold the rudder stick to the right and set it to 70%. This will set how fast the helicopter rotates. You may want it faster or slower so change the value appropiately.
  First make sure the 'B' switch (the front switch on the top/left) is flipped up. Next disconnect the rudder link from the servo. Turn on the receiver. Wait 4 seconds for the gyro to initialize. It may or may not initialize correctly depending on where the gyro channel reverse setting is set in the radio. Remember the gyro has to start up in HH (Heading Hold) mode. Continue with the next step to determine if it's in the right mode.
set to start up in HH Move the rudder stick to the right, then back to center, if the rudder servo does the same then you are in normal mode which is wrong. If the servo moves to one direction but does not move back to center then you are in heading hold mode which is right. If you ended up in normal mode then flip switch 'B'. Then turn off the receiver and then back on and let the gyro initialize in heading hold mode.
set to normal mode Now that you have the gyro initialized correctly, flip the 'B' switch the other direction. This will make the gyro go into standard rate mode.
servo direction Check the servo direction. Move the rudder stick to the right and watch the servo arm. It should move the servo clockwise which thereby should pull the rudder control link forward. This will make the nose of the helicopter rotate to the right. If not, then go to the 'REVERSE' menu and change channel 4.
gyro direction Rotate the helicopter so the nose goes to the left and watch the rudder servo. The servo needs to rotate clockwise. If not, then flip the reverse switch located on the top of the gyro.
With the rudder link disconnected from the servo. The first thing to do is make the link slide as free as possible. Adjust the guides to acheive the least resistance. I added a slight bent to the front section of the rod as you can see if you click on the photo to the left. I did this so as to stop the resistance the rod had on the first frame guide due to being pulled down to the servo. I also use a JR Ball link resizing tool to remove unecessary resistance from the ball links. Once you get the link as free from resistance as you can. You need to take off the rudder servo arm and install/move the ball to a position that is about 13mm from the center. The instructions with the gyro say to use the recommended distance that the helicopter instructions say to use. I used the 13mm position and found it to work great. A friend tried a much longer distance and it did not work as well. Next set the rudder servo arm back on the servo so that it points up with the rudder stick and rudder trim centered. The best position for tail centering is to adjust the rudder link so that you have 4.5mm between the pitch slider and the tail rotor casing (see the picture to the left). Another way to find center other then measuring 4.5mm is to visually align the control arm to be parallel with the tail shaft. Check that the front link is centered with the ball on the servo arm. If it's not, turn the link clockwise to move it toward the back or counter clockwise to move it forward. Once the center of the ball link matches with the center of the ball and you have the 4.5mm at the tail slider, then you can move to the next step.
  First make sure the 'Limit' on the top of the gyro to it's max (140), while you're adjusting that go ahead and make sure the 'Delay' is set to 0 if you are using the 9253 servo, otherwise start around 30 and later experiment to find the best value for the servo you use.
Hold the tail rotor stick full right and pull the control rod all the way forward. Pull the link as far forward as it can go then adjust the 'Limit' control on the top of the gyro so that the ball on the servo arm centers with the link. Once you are finished you can snap the link on the ball.
Set back to HH Now that you're done with that, you need to flip the 'B' switch back to heading hold mode.
Notes about the gyro HH/Standard Rate With the GY401 there is very little reason to use standard rate mode. I leave mine in HH all the time. On other gyros I would prefer to have Normal flight mode use standard rate because the HH mode would have a kinda jerky non-fluid motion when doing ground maneuvers such as slow piroueting circles. With the GY401 I have found it is smooth all the time in HH mode so I just leave it there.
Flying adjustments To get the tail to move faster or slower, adjust the rudder channel travel. Go to the 'E. POINT' menu and set 'RUD' left and right. A higher value will make the heli pirouette faster and a lower value will make the tail slower.
Also if you are using a servo other then the 9253 then you may need to adjust the Delay pot on top of the gyro to stop the tail from wagging after a quick stop.
If you the tail wags in a hover then decrease the gain. Go to the 'GYRO SENS' menu and decrease the value of the up rate if wagging in HH or down rate if wagging in standard rate mode.
Symptom Cause
Gain values have to be set low to stop any tail wagging. 1. The helicopter is out of balance. Vibration is the cause of low gain settings. Check the blades, check for bent main shaft, spindle shaft, tail shaft, out of balance tail blades, etc.
2. I found that a sticky clutch caused me to have to turn down my gain by 20%. Check the
engine/start shaft alignment and look for a broke shoe.
3. The ball on the rudder servo is too far away from the center.
HH doesn't hold good 1. The RPM's should be 1850 to 1950 for 3D flight. It's also important that your engine is running good. If your engine loads up a lot then you won't be able to keep a consistent RPM. Remember that a few hundred rpm drop on the head is several hundred rpm drop on the tail.
Tail wags only right after a pirouette, or anytime I move the tail then stop. If you are using the 9253 servo then you probably have some resistance in your tail control rod. Make sure the guides are aligned for least resistance. Also keep your tail shaft oiled. If it is dry and tacky this will cause the problem.
If using a servo other then the 9253 then increase the value of the delay (pot on top of the gyro).